The design of a commercial electronic device uses, for example, a Computer Aided Design system for designing the layout on a printed wiring board. For this purpose, arranging parts on the printed wiring board and wiring between the parts arranged on the printed wiring board are designed.
In cases where a through-hole via is used for arranging parts on the printed wiring board and for connecting layers, a line (wiring pattern) having a predetermined line width is formed between lands of through-holes. Here, a land is a round-shaped pattern formed around a via to place a lead of a part to be arranged or around a hole that connects layers.
In designing the wiring on the printed wiring board, a fillet process that forms a fillet 4 at the connection between a straight line 2 and a round land 3 on the print wiring board 1 is sometimes carried out to inhibit a via connecting conductor that enhances the reliability of connection from peeling off as illustrated in FIGS. 46-49. A fillet is also called a “teardrop”. One of the known shapes of a fillet 4 is a sector shape having straight lines on the both sides and widening from the straight line 2 to the round land 3 (see Patent Literatures 1-4 below). The reference number 3a in FIGS. 46 and 47 represents a through-hole via (also simply referred to as “via”).
In executing the above fillet process during designing the wiring on the print wiring board 1, the designer assigns various shape parameters of a fillet 4 for each part to be designed as illustrated in, for example, FIGS. 46-49, so that a fillet 4 determined in terms of the shape parameter is formed for the part.
In the first example of FIG. 46, the length L of the fillet 4 is assigned to the shape parameter. The length L represents the distance between an intersection at which the both side lines of the fillet 4 cross the straight line 2 and the outer circumference of the land 3. The both sides of the fillet 4 are in contact with the outer circumference of the land 3. A region surrounded by the both sides of the fillet 4, the outer circumference of the land 3, and the straight line 2 is defined as the fillet 4.
In the second example of FIG. 47, the ratio R (length/width) of the length to the width of the fillet 4 is assigned to the shape parameter. In this case, the value of the width W of the fillet 4 is provided previously and the length L of the fillet 4 is calculated by multiplying the width W and the assigned ratio R (L=W×R). Accordingly, the length L becomes larger in proportional to increase in the width W. Then, the fillet 4 is generated on the basis of the calculated length L in the same manner as the first example of FIG. 46. Here, an example of the width W is a value obtained by subtracting the predetermined line width of the line 2 from the diameter of the land 3.
In the third example of FIG. 48, the angle θ formed by both sides of the fillet 4 and the offset L are assigned to the shape parameters. The offset L corresponds to the length of the fillet 4 in the above first and second examples. In this example, a fillet having an offset L between the line 2 and the land 3 and having both sides forming the angle θ is generated.
In the fourth example of FIG. 49, a length rate r is assigned to the shape parameter. The length rate r represents the distance between the end point of the straight line 2 (starting point of the fillet 4) and the center of the land 3. In this example, the radius of the land 3 is provided previously and the position of the starting point of the fillet 4 with respect to the land 3 is determined by multiplying the radius and the assigned length rate r. Two tangents passing through the starting point and being in contact with the outer circumference of the land 3 are calculated as the both sides of the fillet 4.